Baader Classic Ortho - Initial impression

The new Baader classic ortho became recently available, I got the 10mm focal length a few days after Christmas. According to Baader it replaces the Baader Genuine Orthos (BGO). The price of the BCO is significantly lower than that of the BGO, 55 Euro compared to 95 Euro for the BGO which are not available any more.

which indicated very a promising performance. What I am presenting here is an initial impression of the performance of a production eyepiece based on daytime observations with a very small f/6.5 mm refractor. The eyepieces comes with a winged rubber eyecup. Its apparent field of few is almost 50 degree (measured field stop diameter 8.7 mm), this significantly larger than that of other orthos. I have compared the 10 mm BCO with the 9 mm BGO and the 12 mm Kasai HD ortho which seems to be essentially identical with the 12.5 mm BGO. The built quality is on a little bit lower than that of the BGO, but very reasonable in view of the low price.
The eyelense of the 10 mm BCO is larger than that of the 12 mm Kasai, eye placement is very easy and comfortable. Since the focal lengths are not identical I can give only a very general impression. In the center the image is very crisp, the background (artifical star) is quite dark, scattered light is well controlled, comparable to the BGO. At the outermost edge the image gets a little bit soft. The coatings are very nice, they seem to me at least as dark as that of the BGOs. The transmission at 532 nm wavelength is very good, I measured 97 % (compared to 96.-96.8 % for the Zeiss Abbe 10 mm between 500 and 550 nm wavelength taken from the table by M. Ludes).

In summary, the 10 mm BCO is an excellent ortho eyepiece, optical on the same level as the BGO. Personally, I find the larger AFOV very nice.

The off-axis should be soft...by design! Baader extended the field stop to open it up to a wider 50 degrees. Concept was to give larger FOV to make finding easier. The design was not changed to better correct this extra off-axis since only intent was to assist newbies to locate targets easier and move them into the sharper traditional 42 degree zone of an Abbe.

Thanks for the review! Sounds great, especially since it appears that the Circle T orthos are almost kaput. It will be interesting to directly compare these BCOs to the Circle T/UO Abbe Ortho/KK volcanos and the soon-to-be-released Kasai HC Orthos (BGO/UO HD clones).

Just a speculation as to why the Classic plossl 32mm might have a narrower than 50-deg. AFoV - the lenses can be about as large as what the body’s barrel dimension will permit. In order to get a larger field, a larger barrel would be needed, and probably a different eyecup too, which would equate to higher cost for larger lenses. Such is also the case with the Clave 30mm plossl if not mistaken. The Barrel OD may be similar to the Classic Plossl, and the field size would be about 45-deg too, whereas the shorter Clave focal lengths had 50-deg fields of view just like the BCO's. To keep the selling price within reasonable limits, there are plenty of design tradeoffs and considerations applied, and these may possibly be the reason for the narrower FOV for the Classic 32mm plossl.

I never thought it would happen...the demise of the Circle "T"'s is a sad time.

Guys, what falls into that category? Just cant remember what Circle T stands for ....

Thanks

Radim

Circle-T (Tani) was the workshop that produced many of the Japanese orthos, kellners, and erfles that were sold since about 1970 (?) under various labels: University Optics, Kokusai Kohki, Orion, Coulter, Edscorp, Celestron and others.

For many like myself, the UO abbe orho is perhaps the best known and the most emblematic Circle-T product. We knew they were produced by a small shop but never expected them to be "no longer available".

A separate thread on all the Circle-T models and their various re-seller brands would be timely.

My first impression, the 10 mm BGO is gives very plaesing views. Great contrast, black sky background and razar sharp in the center. With an aparent field of view of 50 degree it can also be used for deep sky viewing. It differs substantially from the tunnel view of many other orthos. Sure, at the edged the image is slightly soft.

All in all, the image quality is very similar to that of the 9 mm Baader Genuine Ortho.